1883.J Variations of Latency in certain Skeletal Muscles. 287 



support of this we may mention that the shortest latency referred to 

 occurred in a curarised, the longest in a non-curarised muscle. In 

 the case of the toad, variations due solely to the individual were con- 

 siderable, but the divergencies were not so great as in the case of the 

 frog. Thus in six gastrocnemii taken from different individuals the 

 range was from *0125" to '01 7", in the triceps (six muscles) from 

 •012" to -015", and in the hyogiossus -015" to -024". We seldom 

 found any material difference in the latencies of corresponding muscles 

 in the same animal. The toads examined in December and January 

 yielded latencies averaging '0121" (triceps) and '0191 " (hyogiossus 

 and rectus abdom.), whilst the March animals gave '0128" (triceps) 

 as the shortest, and '015" (hyogiossus and biceps) as the longest 

 latencies. The subjects of the latter experiments were unspawned 

 animals, and the reaction of the trunk muscles was marked by an 

 accession of irritability. 



In the tortoise, the long parallel fibred muscles, omohyoid and 

 semibranosus, yielded the shortest latencies, viz., *0225" and '0247" 

 respectively, whilst the wide bellied biceps and the broad but short 

 extensor communis digitorum gave distinctly longer periods ('028" 

 and "033"). The gastrocnemius of a kitten, aged two months, showed 

 a latency of '018", and that of a white tame rat '011". 



In the pigeon the pectoralis major has a slightly shorter latency 

 (•01") than the gastrocnemius, but in the blackbird the biceps (a muscle 

 intimately connected, as is the pectoralis, with flying movements) 

 appears to have a latency longer by '0015" than the gastrocnemius of 

 the same bird. It is worthy of remark, however, that the blackbird 

 had been reared and kept in confinement, and therefore it is probable 

 that the muscles connected with flight were to a certain extent 

 uneducated and undeveloped. 



To sum up the variations in latency obtained between the frog 

 muscle, which, free from exceptional influences, yielded the shortest 

 ("008"), and the tortoise muscle, which yielded the longest ('033"), we 

 have but a range through '025", a variation small enough to be in itself 

 surprising, but still more so when we consider the relative durations of 

 the contractions to which these latencies are initial. We may certainly 

 infer from these results that, though the intralatent processes in the 

 various muscles of a given animal have a certain inter-relationship 

 with the resulting contractions, and that each muscle variety gives 

 divergencies from its normal latency and contraction only within 

 certain limits, that we can establish no argument of probabilities from 

 an animal of one species to an animal of another species as regards the 

 latency preceding contraction. The same holds true of warm-blooded 

 as well as of cold-blooded, of Carnivora as of Rodentia. 



The literature published during the last twenty years relating to the 

 duration of the latent period, bears witness to the very different lines 



